I originally thought of this idea when asked to make a proposal for a sculpture competition that was to be held by the sea. It seemed to be a little conservative, and you had to show detailed sketches before being allowed to enter.
Anyways, the idea was to have this wooden platform set into the grass
by the beach about 3m x 3m in size. Three walls would be affixed, with no roof, and lining the walls would be traditional landscape paintings. Underneath the platform, weight sensors would indicate when several people were on the platform looking at the paintings, which would then prime what was in fact a huge catapault. The arm part would be hidden just under the surface of the beach, the pivot at a distance for the mechanics of the trap to effectively fling the 'art lovers' far out to sea. The catapault would then be pulled back down into place, to await the next group of unsuspecting conservative patrons.
As a multi purpose trap, one would only have to take out the paintings and 'bait' the trap in relation to the desired catapaultee. They could be set up all across the country, and the sight of people being jettisoned far out to sea/across state lines would be commonplace.
A normal picnic table fastened to the platform would rid your area of unwanted tourists.
Unwanted cars parking in your space, thrown back to where they came from.
This idea could be modified for armed hold ups - the catapault platform being just in front of the counter.
Annoying charity collectors, the elderly, joggers, children at the playground - return them all from where they came!